Vibrated refrigerated surface

ABSTRACT

Apparatus for chilling a liquid to produce a slurry includes three coaxial lengths of tube meeting in a junction, one of them being torsionally sonically vibrated and another, which chills the liquid, contacts the liquid on one of its sides and a refrigerant on the other. Extremities of the lengths of tube are supported at nodal points and the junction is at an antinodal point if the vibrated and chilling lengths of the tube are of different diameters. The design is robust whilst avoiding large losses of sonic energy.

United States Patent lnventors Jeffrey Stuart Kenworthy;

Hans Berthhold Wiener, Stockton-on-Tees England Appl. No. 849,066 Filed Aug. 11, 1969 Patented May 4, 1971 Assignee Imperial Chemical Industries Limited London, England Priority Sept. 5, 1968 Great Britain 42217/68 VIBRATED REFRIGERATED SURFACE [56] References Cited UNITED STATES PATENTS 3,224,213 12/1965 Hoyt, Jr 62/68 3,411,309 11/1968 Skrebowski et al 62/ l 23X Primary Examiner-William E. Wayner Attorney-Cushman, Darby and Cushman ABSTRACT: Apparatus for chilling a liquid to produce a slurry includes three coaxial lengths of tube meeting in a junction, one of them being torsionally sonically vibrated and another,

12 Claims 2 Drawingfigs which chills the liquid, contacts the liquid on one of its sides US. 62/72, and a refrigerant on the other. Extremities of the lengths of 62/ 123, 165/84 tube are supported at nodal points and the junction is at an an- Int. Cl F251: l/l2 tinodal point if the vibrated and chilling lengths of the tube are Held otSearch 62/68, 72, of difierent diameters. The design is robust whilst avoiding 340, 353, 123; 165/84 7 large losses of sonic energy.

a 1 17 A Z 7 V 5 1 a VIBRATEI) REFRIGERATED SURFACE This invention is concerned with refrigeration.

In processes for freezing liquids, for example, those comprising paraxylene and at least one other xylene and/or ethyl benzene, to produce slurries comprising a mother liquor and crystals by contacting them with a chilled surface it is desirable to vibrate the chilled surface with sonic vibrations in order to prevent the build up of solid deposits on the chilled surface.

In order to maintain a satisfactory intensity of vibrations at the chilled surface it is desirable to prevent as far possible the loss of sonic energy from the chilled surface by conduction to other parts of the apparatus used. This may be achieved for example, by flexibly supporting vibrating parts and feeding the liquid or refrigerant to them through bellows as described in United Kingdom Patent specification No. l,l04, 508. Such construction however involve a number of design difficulties; for example bellows are inherently weak.

According to the present invention apparatus for chilling a liquid to produce a slurry comprises a first length of tube of thermally conducting material adapted to contact on opposite sides a refrigerant and the liquid to be chilled, thus constituting a chilled surface, second and third lengths of tube substantially coaxial with the first, each secured at one end to the same end of the first length of tube, the second length defining with the first length boundaries of a vessel holding refrigerant or liquid, and means for torsionally sonically vibrating the second or third lengths of tube, the said means being separated from the liquid or refrigerant by the said second or third length of tube, wherein the length of tube which is vibrated has the same diameter as the first length of tube or the junction between the lengths of tube is at an antinodal point; and rigid supports for free extremities of the lengths of tube at nodal points.

According to a further aspect of the invention, a process for v chilling a liquid to produce a slurry in the apparatus comprises contacting the first length of tube with the liquid on one side and with a refrigerant on the other side, torsionally vibrating the second or third lengths of tube and recovering slurry from the apparatus.

The sonic vibration may be in the range of 0.5 to 30 and preferably 8 to kilocycles per second.

In the apparatus of the invention vibration will tend to be reflected from the rigid supports and will thus be retained within the vibrating parts of the structure. The tubes themselves may if desired by continued beyond the rigid supports, or these may be at the ends of the tubes.

When the vibrated length of tube has the same diameter as the first length of tube it constitutes an extension of that length of tube; the junction may be made in such cases from three tubes, two of which have the same diameter or preferably from two original tubes of different diameters by welding one tube circumferentially at one end to the other tube.

Apparatus according to the invention may be constructed in a wide variety of ways. The rigid supports of the first and second lengths of tube may be e'nd-plates defining boundaries of a refrigerant tank comprising a number of similar systems, or they may be the end walls of an, individual refrigerant jacket.

In one form of the invention a thermally conducting tube adapted to contact a refrigerant on its outside is rigidly supported at its ends and united to an intermediate antinodal point with a coaxial internal tube which is provided with means for torsionally vibrating it. ,The lengths of the thermally conducting tube on either side of the junction thus constitute the first and second lengths of tube. Liquid to be chilled in this form of the invention is passed through both the first length of tube and the internal tube. Alternatively, a thermally conducting tube mounted between rigid supports bay be united for example at an antinodal point to a coaxial external sleeve which is united to a further rigid support at a nodal point, the latter rigid support and one of the supports for the thermally conducting tube defining boundaries of a refrigerant jacket or the refrigerant jacket or tank being provided with means for torsionally vibrating it.

Refrigerants for cooling the chilled surface may be cooled in any refrigeration device, which may be of conventional design. The refrigerant may be for example, ammonia, ethylene, ethane or carbon dioxide. Suitable refrigerants however when only moderately decreased temperatures are required are brine, petrol, methanol and acetone, or preferably a pentane, for example, n-pentane.

A number of the refrigerants for chilling the surface (for example ammonia, ethylene, ethane and carbon dioxide normally evaporate in the chilling process, and thus produce a boiling effect, though this can be suppressed by using high pressures. Refrigerants of this type are particularly appropria'te for the production of low temperatures, which are used in the treatment of mixtures comprising paraxylene and one or more other xylenes and/or ethyl benzene containing only small concentrations (for example of 1030 and more usually 15-25 per cent by weight) of p-xylene.

Suitable chilled surfaces are of any metal resistant to the temperatures employed in the process, having a high thermal conductivity and a low attenuation of the sonic vibration, for example, aluminum and its alloys, many copper alloys, especially the copper/beryllium alloys and brass, but preferably steels, for example stainless steel.

The source of the sonic vibrations may be for example a piezo electric device, or a generator for electric current, together with a coil connected across the generator and surrounding a core of magnetostrictive material, the source being coupled tangentially either directly or indirectly, for example through a velocity transformer to amplify the vibrations to the tube to be vibrated. Sources may be coupled to one or more,

and preferably at least three radial steps of a ring secured to the tube.

Coupling of the core and/or velocity transformer to a vibrating part of the apparatus may be achieved by welding.

Preferably the sonic vibrations have a power of, for example, l to 500 watts of acoustic power per square foot of the chilled surface. In general from 2 watts per square foot and at most 100 watts per square foot are usually used.

It is preferred that the liquid to be chilled should be located on the inside of the first length of tube and to surround the first length of tube by refrigerant.

The surface of the first length of tube contacting the liquid may be at a temperature in the range of 5 to 50 Centigrade degrees and preferably 10 to 30 Centigrade degrees below the temperature of the liquid being chilled at its crystallization point. A preferable difference is 15 to 25 C. In general, the greater the temperature difference, the greater the power of the sonic vibrations required. In the case of mixtures of paraxylene and one or more other xylene and/or ethyl benzene the greater the concentration of p-xylene, the smaller the temperature difference which is practical.

Preferably the surface of the first length of tube contacting the liquid is polished.

It is desirable that the liquid should be flowed through the first length of tube. It is preferred that the linear flow rate should be at least six inches per second, and that flow should be turbulent. The liquid may, if desired, be stirred.

One form of the invention will now be described with reference to the drawings in which FIG. 1 shows an elevation of an apparatus according to the invention.

A 6-inch internal diameter straight tube 1 12 ft. long having a wall thickness of 0.128 inch is secured at one end into tube plate 2 and at a point 10 feet along the tube from tube plate 2 into a second tube plate 3. The tube plates are of the following dimensions; 15 inches external diameter bored out to fit the tube 1 and 1.375 inches thick. A further tube 4 of internal diameter 8 inches surrounds tube 1 thus defining a refrigerant jacket; and inlet 5 and an outlet 6 are let into the tube 4.

An internal tube 7 is welded by means of a spun flange at one end to the internal circumference of tube 1 at a point 12 tank, the length of the thermally conducting tube lying outside inches from the tube plate at its end. The internal tube is concentric with tube 1 and is provided with a drive ring 8 24 inches from the weld and 12 inches from its other end on which ring 8 are mounted tangentially 8 magneto-strictive transducers in four pairs designed to operate at a frequency of 2.5 to 8 kilocycles per second and at an electrical input of 500 watts. The internal tube 7 has an internal diameter of inches and a wall thickness of 0.250 inches.

At the free ends of tubes 1 and 7 flanges 9 and are provided to facilitate connection of the tubes to further apparatus. The flange l0 and tube plate 3 are situated at nodal points in order to prevent the transmission of vibrations through it to other parts of the apparatus, but it is unnecessary for the flange 9 to be at a nodal point. The length of tube 1 between tube plate 3 and the junction with tube 7 is the first length of tube, the length of tube 1 between the junction with tube 7 and tube plate 2 is the second length of tube and tube 7 is the third length of tube.

The apparatus is operated by passing the liquid to be chilled through the inner tube and passing refrigerant through the outer tube whilst operating the transducers to provide a torsional vibration having a frequency of for example 2.67 or 8 kilocycles per second using a wave-length of 48 inches or 16 inches respectively.

The internal surface of the tube 1 from the junction of the spun flange of the 7 to tube plate 3 is highly polished.

FIG. 2 of the drawing shows an elevation of an alternative form of apparatus according to the invention wherein tube 7 has the same diameter as tube 1. Common reference numerals are used in FIGS. 1 and 2 to define the same elements, it being noted that 9a and 10a represent rigid supports.

We claim:

1 Apparatus for chilling a liquid to produce a slurry which comprises a first length of tube of thermally conducting material, means for contacting the first length of tube on opposite sides with a refrigerant and the liquid to be chilled, second and third lengths of tube substantially coaxial with the first length of tube each of the second and third lengths of tube being secured at one of their ends to the same end of the first length of tube, a vessel for holding refrigerant or liquid of which the second length of tube and the first length of tube define boundaries, and means for torsionally sonically vibrating one of the second and third lengths of tube the said means being separated from the liquid and refrigerant by the lengths of tube, wherein the length of tube which is vibrated has the same diameter as the first length of tube or the junction between the lengths of tube is at an antinodal point; and rigid supports for free extremities of the lengths of tube at nodal points.

2. Apparatus as claimed in claim 1 in which the means for torsionally sonically vibrating the second or third lengths of tube produces such vibrations at a frequency in the range 0.5 to 30 kilocycles per second.

3. Apparatus as claimed in claim 2 in which at least one of the tubes extends beyond the rigid supports.

4. Apparatus as claimed in claim 2 in which the rigid supports of the first and second lengths of tube are the end walls of a refrigerant jacket for the apparatus.

5. Apparatus as claimed in claim 1 in which the means for torsionally sonically vibrating one of the second and third lengths of tube comprises a ring secured to said tube which ring has at least three radial steps and sources of sonic vibration coupled to the steps tangentially to the tube.

6. A process which comprises chilling a liquid to produce a slurry in an apparatus as claimed in claim 1 by contacting the first length of tube on one side with the liquid and with a refrigerant on its other side, torsionally sonically vibrating one of the second and third lengths of tube and recovering a slurry from the apparatus.

7. A process as claimed in claim 6 in which the sonic vibrations have an acoustic power of 1 to 500 watts per square foot of the surface of the first length of tube.

8. A process as claimed in claim 6 in which the surface of the first length of tube contactinothe li uid to be chilled is at a temperature in the range 5 to C. low the temperature of the liquid being chilled at its crystallization point.

9. A process as claimed in claim 6 in which the liquid to be chilled is located on the inside of the first length of tube.

10. A process as claimed in claim 9 in which the liquid is flowed through the first length of tube.

11. A process as claimed in claim 10 in which the flow is turbulent.

12. A process as claimed in claim 6 in which the liquid which is chilled is a mixture of paraxylene and at least one other xylene and/or ethyl benzene. 

2. Apparatus as claimed in claim 1 in which the means for torsionally sonically vibrating the second or third lengths of tube produces such vibrations at a frequency in the range 0.5 to 30 kilocycles per second.
 3. Apparatus as claimed in claim 2 in which at least one of the tubes extends beyond the rigid supports.
 4. Apparatus as claimed in claim 2 in which the rigid supports of the first and second lengths of tube are the end walls of a refrigerant jacket for the apparatus.
 5. Apparatus as claimed in claim 1 in which the means for torsionally sonically vibrating one of the second and third lengths of tube comprises a ring secured to said tube which ring has at least three radial steps and sources of sonic vibration coupled to the steps tangentially to the tube.
 6. A process which comprises chilling a liquid to produce a slurry in an apparatus as claimed in claim 1 by contacting the first length of tube on one side with the liquid and with a refrigerant on its other side, torsionally sonically vibrating one of the second and third lengths of tube and recovering a slurry from the apparatus.
 7. A process as claimed in claim 6 in which the sonic vibrations have an acoustic power of 1 to 500 watts per square foot of the surface of the first length of tube.
 8. A process as claimed in claim 6 in which the surface of the first length of tube contacting the liquid to be chilled is at a temperature in the range 5* to 50 * C. below the temperature of the liquid being chilled at its crystallization point.
 9. A process as claimed in claim 6 in which the liquid to be chilled is located on the inside of the first length of tube.
 10. A process as claimed in claim 9 in which the liquid is flowed through the first length of tube.
 11. A process as claimed in claim 10 in which the flow is turbulent.
 12. A process as claimed in claim 6 in which the liquid which is chilled is a mixture of paraxylene and at least one other xylene and/or ethyl benzene. 